The User / Access Management endpoints allow you to configure the people, roles, and organizational structure that interactions are associated with. Before uploading interactions for analysis, most organizations will use these endpoints to establish their hierarchy structure and ensure agents and users are correctly set up.
The three resource types are related: hierarchies define your organizational reporting structure; users are the people who access the platform; and agents are the contact center representatives whose interactions are captured and analyzed. Users and agents can be linked, and linking hierarchies to users defines the data that user can access.